1. Field of the Invention
The present invention relates to a pelletizer for pelletizing a material. In particular, the present invention relates to a pelletizer for pelletizing a water-dispersible, which includes totally water-soluble, melt-extrudate.
2. Description of the Related Art
Melt-extrusion is an advantageous method for producing water-dispersible granular agricultural compositions. See, e.g., published PCT application number WO 9215197. One limitation to the commercial exploitation of this technology involves the inability of known pelletizers to pelletize water-dispersible melt-extrudate, since they are designed for use with water-insoluble materials and use water as a cooling medium. Typical of such pelletizers are those described in U.S. Pat. No. 3,341,892 to Maynet, in U.S. Pat. No. 3,753,637 to Gasior et al. and in U.S. Pat. No. 5,186,959 to Tanaka. Water-cooling is obviously unsuitable for water-dispersible melt-extrudate. Operation of such known pelletizers without any cooling would result in rapid fouling of the pelletizer, resulting from pellets being adhered to the pelletizer. Attempting to operate such known pelletizers by simply using air in place of water would be unsuccessful, because the cooling achieved by air is inadequate.
Pelletizers which use air cooling are also known. For example, Japanese Unexamined Patent Application Publication No. 5-169,441 discloses a pelletizer for pelletizing hot resin which has spraying holes formed in a nozzle die which spray a coolant, such as air, from the die face. The die face is disposed at the outer periphery of the rotor, and the cooling air is delivered in a radially inward direction. U.S. Pat. No. 4,212,617 to Bagdan et al. discloses an apparatus for cutting cheese strands which delivers cooling air through passages disposed in a shaft. The cooling air is delivered to an inner edge of a knife assembly, which is spaced from the cutting edge of the knife. Thus, although the devices of both Publication No. 5-169,441 and Bagdan et al. provide a way to cool the knives, neither device aids in sweeping the pellets off the knives in a configuration which prevents fouling of the pelletizer. To the contrary, in both these devices, as the rotor on which the knives are mounted rotates, centrifugal force causes the pellets to be flung out in all directions in the interior of the pelletizer, contributing to fouling of the pelletizer.
Thus, there exists a need for a pelletizer which is able to pelletize water-dispersible melt-extrudate and which, at the same time, aids in sweeping the pellets off the knives in a configuration which effectively prevents fouling of the pelletizer.